Figure 3.

Membrane and aqueous dye mixing activity of WT HA and the HEE, HPP*, and HHP* chimeras. All constructs induced R18 to redistribute from RBCs to cells expressing the constructs (left panel). The cytoplasmic marker (CF) transferred efficiently for WT HA and HEE- and HPP*-expressing cells (right panel), demonstrating fusion. In contrast, HHP* only supported limited transfer of a membrane dye without transfer of aqueous dye, suggesting that it caused hemifusion. RBC ghosts colabeled with R18 and CF were bound to HA cells, and fusion was triggered by a 2-min application of pH 4.8 buffer at 37°C, followed by incubation for 5–8 min at neutral pH before microscopically examining cells.